trane xe80 diagnostic code

I have a trane xe80 furnace in my shop. I turn the power off to it when it's not being used. The last time I turned it on,the small fan came on as always and kept running,but the furnace never tried to light. The diagnostic led blinks 4 times. It says that the thermal protection device is open. I looked on the wiring diagram and can't find what or where this is. Can someone please tell me what I'm looking for here and what could be the cause? Thanks for any information about this problem.

 

Thermal protection device, probably labeled as a roll out switch in your wiring diagram, there are a few in most cases. you will find them near the burners, small round disc with 2 wires hooked to each one, there is also a button in the middle that is manual reset. push down on all of those buttons with the power off, or if you have a multi meter check to make sure you have continuity across each one as well as the limit switch which is going to be mounted above the burners and below the inducer fan, should be a square/rectangle about 2inches with 2 wires hooked to it mounted to the furnace vestabule. once youve verified continuity with all those then reset power and see what happens. If the furnace is a downflow there will be a thermal limit inside of the blower cabinet as well mounted on the fan housing. once you reset everything and the flame come on check to be sure it is not delayed at all causing a flame roll out which would trip one of those sensors, this is usually causes by the burners being dirty from particles in your shop. if thats the case pull them off clean them up with some water and a brush, and then remount them making sure they are sitting level together for best flame transfer on fire off.